Copolymeric vinylidene chloride composition



Patented Aug. 2, 1949 This invention relates a specific composition .1; IQ-CQ 'I Q W QN Y, FHugo L. sweeter, Midland; Mien, munch The. Dow Chemical Company; Midland; Mich" l m'l ration oi'iDelawai-e:' l b nit-war: jeilimcauoii unio ist, 194':

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consisting or a; particular. vinylidene chloride l vinyl chloride rcopolymer iand smallamounts "oi certain modifying agentstherefor. it relates in particular to such a composition, capable of being extruded and stretched in normahma'nnefto produce transparent, odorless filmswhich arenot dlsclored by the heat of extrusiomare highly resista-nt to discoloration on exposure to light, and which do not exude. their contained modiiying agents.

Within the past few yearsthe copolymers -of vinylldene and vinyl chlorides have become in dustriallyimportant. Some of them'are unique by virtue of their now well-knowncrystalllne' character; Of these, the most importantcopolymers have been'those which may be obtained by polymerizing, in aqueous suspensionja mixture of about 85 per cent by weight of vinylidene chloride and about 15 per cent' of vinyl chloride, under conditions to yield a copolymer' of about 88-94 per cent of vinylidene chloride copolymerized with about 1245 per cent of vinyl chloride. This range of products may-be extrudedreadily when properly modified, but cannot be extrudedgto form useiul products without having present a and stretching ln ithe" m nner is nowjw'ell known. "Suchexudation'glves' the 'rticlean'hn desirablybily surface; This especiallynoticeable with "militi -directionally stretche thin (0.005"inch,f or less)" 'made' fronythe 'described copolymer; asfsuch "film; dueto the arrangementot the submicros'copic crystallitesj,

hasa minimum capacity for internal'inodifiers. Most plasticizers used with thecopolymer, which have the faculty of assisting the extrusiom'have distinct and' commonly disagreeable'" odorsi'and films of the present copolymercbntaining them modifying agent to serve as a plasticizer during the exposure to hightempera'tures in thefextrusion zone, and-to depress the softening pointand increase the thermal stability. Without such agents, the product decomposes at elevated temperatures to such an extent as to'discolor it and make the extruded article 'unacceptablefor'com-' lmercial use. The modifier should have, as well; a protective effect against the action of direct sunlight, which tends to darken the extruded article to unacceptable shades. p It has been the prior experience that very'few' of the common "plasticizers can be used to assist in extrusion of the identified 'copolymer, and that whenthin extruded articles 'Sllh as films or fine filaments are to'bemadethe numgi her of operative plasticizers is still smaller. with most suchmodifiers, the heatof extrusion results in a thermal degradation of the copolymer, evi-"' denced by darkening and by evolution of hydrogen chloride, indicative of decomposition. The resulting products are often brittle, and are subject to further darkening'when exposedto light containing ultra-violet radiations "lhose few plasticizers which have been, used successfully with the present copolymer, notable among which is di-(alpha-phenylethyl) ether, have ex-" uded tothe surface of the crystalline artlcljefaf terj it has been-- formed by H extrusion; supercooling usually exhibit these odors to an even more pro nounoed extent and cannotbeused for packaging foodstuffs because oithe fact that they, impart foreign flavors or odors some enclosed food's Since the described copolymer, "w en in the form of a film; has the lowest moisture vapor trans mission values of any commercial film (from .0.5 n50.1- the valuesior thefbest other films) I itis highly desirable tofind a means for extruding the copolymer without danger or subsequent exudation and the other named. prior disadvantages.

- The defined ran'gbt ta-yeas s;Cincinnati chloride copolymershis unique in its properties and" m the. problems which it presents during extrusion. Larger amounts of v vinyl, chloride] in.

the copbly ner' increase its compatibility with plasticizers and decrease its. extrusionmtempera ture, butare accompanied by increased sensie tivity to organic solvents and films'made'therefrom are less strong and lesscrystallinethan those here concerned. Similarly, lesser amounts of vinyl chloride injthe copolymer are. accompanied by higher fusion temperatures, decreased tlexibility, in extruded articlea' almostcomplete object to provide a thin oriented crystalline-film of the saidcopolymer, which fllm possesses the incompatibility ,lwith plasticizers, and relatively verylimitedlifllity, l i

It is accordingly amon -the objectsof the present invention to provide-a composition of'mat- :ter, containing {the above-identified ,copolymer and suchadjuvants as may be required toextrude the fsame easily without thermal; decomposition;

which is capable of being extruded and, stretched to form an oriented crystallineithimfilm which 'isclear and transparent, odorless, doesnot exude said adjuvants on standing, either at room. teme perature or above; and is resistant. to discoloration whenexposedto sunlight. It is anultimate above-stated desired properties. K v

It haslrrow been; found thattheforegoing and re lated objects may be attained by the prepara- 3 tion of a particular composition consisting oi at least 90 per cent and not over about 98 per cent by weight of the copolymer containing from 88 to 94 per cent 01' vinylidene chloride copolymerized with correspondingly from 12 to 6 per cent of vinyl chloride, and complementarily from 10 to 7 per cent in the aggregate oi the following two modifiers in the range oi. propo tions stated: (1) from 2.5 to per cent of 3-(2- xenoxy) -1,2-epoxy propane and (2) from 2.5 to 5 per cent of 4'-tertiary-butyl phenyl salicylate. The so-defined composition is compatible, not only at the elevated temperatures encountered during extrusion operations, but also in the oriented product at the above room temperature after extrusion, so that extruded articles show no tendency to exude the contained modifiers, and have no oily appearance or feel. Even when the extruded article is a fine fiber or a thin film, it exhibits no significant odor, and such films may be used without danger to wrap cheese, butter or other i'oodstufi's which are very receptive 01 foreign tastes. Such films are relatively unafiected by sunlight, as evidenced by the fact that when exposed to Florida sunshine for 6 months, the films of the present composition had assumed a mild straw tint, while the heretoi'ore commercial film, containing the same copolymer plasticized with '7 per cent of its weight of di-(alpha-phenylethyl) ether acquired a very dark brown to black coloration after about one month.

By way of contrast with the present specific composition, when the previously defined copolymer is modified by any one 01' the present modifiers in quantity sufilcient to permit extrusion, the extruded product, especially in film form, is defective in one or more important respects. Thus, if 3-(2-xenoxy) -l,2-epoxy propane is used alone, such an amount is necessary for extrusion that bleeding occurs from the film, the film has a disagreeable odor, is not stable to light, and the properties of this plasticizer make such exuding films unsuited for ,use. on foods. When 4'-tertiary-butyl phenyl salicylate is used alone extrusion is nearly impossible, resulting films exude the plasticizer as a crystalline bloom, have a characteristic odor, and show signs oi very marked deterioration due to the heat of extrusion.

In a. specific example, a composition was prepared by mixing in. a ball mill 5 parts by weight of 3-(2xenoxy) ,2-epoxy propane and 3.5 parts of 4'.-tertiary-butyl phenyl salicylate with 91.5 parts of a copolymer of vinylidene and vinyl chlorides which was shown to contain 92 per cent of the former chloride copolymerlzed with 8 per cent of the latter. The composition was extruded at 175 C. as a tube 2.5 inches in diameter. The tube passed downwardly into a water bath at 10 C. to supercool it, thence between two spaced pairs of driven pinch rollers. The portion of tube between the orifice and the first set of rollers contained a column of mineral oil to a level slightly above that of the water bath. The section between the two sets of pinch rolls was inflated to provide an elongated bubble, enough air being used to expand the tube radially about four times its original extruded diameter. This stretching occurred between and removed from each of the sets of rollers. Addition of -more air resulted only in elongation of the bu ble and displacement of the stretching zone posed surfaces of toward the first set of rollers, and not in a greater radial distension. The driven rollers had a peripheral speed about three times that or the idler rolls. The resulting film tube was slit in the customary manner to provide a film sheet about 31 inches wide and about 1.5 mils thick. The film was clear and transparent and showed no Signs of yellowing due to the heat of extrusion. Even on prolonged standing the film did not exude its contained modifiers, and had no noticeable or objectionable odor. exposure to sunlight in Florida there was no darkening in one month and only a light straw tint developed in six months. Portions of the film were used to wrap freshly cut blocks of cheddar cheese, and the wrapped product was kept for several days at moderate temperatures permitting the fats in ,the cheese to come into contact with the film. Slices from the six exthe cheese has no detectable foreign flavor. By way of contrast, a similarly produced film consisting oi. the same copolymer and 7 per cent of its weight of di-(alphaphenyl-ethyl) ether had a marked surface oiliness due to exudation immediately after it was produced, a strong and disagreeable persistent odor, and would not be considered for use in contact with odor-sensitive foods. A roll of that film, on standing for a few weeks, actually dripped the exuded plasticizer.

While each of the modifiers oi. the present invention may be used within the range of proportions previously given, it has been found that the aggregate amount of all of them must not exceed 10 per cent of the weight of the composition, and must be at least about 7 per cent of the composition, to be sure of avoiding thermal decomposition during extrusion, darkening due to light, and exudation under a wide range of conditions of storage and use.

It is to be understood that die lubricants, such as carnauba wax or magnesium stearate, may be used in the customary manner during extrusion of the present compositions. Such agents, being used only for their effect in lubrication of the composition through the extrusion die, are not considered essential parts of the composition.

I claim:

1. A composition or matter consisting of from to 93 per cent by weight of the copolymer containing from 88 to 94 per cent of vinylidene chloride and correspondingly from 12 to 6 per cent of vinyl chloride, and from 7 to 10 per cent in the aggregate of the following modifiers, each within the range of proportions stated: (1) from 2.5 to 5 per cent 01 3-(2-xenoxy)-1,2-epoxy propane and (2) from 2.5 to 5 per cent of 4'-tertiarybutyl phenyl salicylate.

2. A transparent, odorless oriented crystalline film, which is resistant to discoloration due to light,and is free from tendency to exude its contained modifiers, composed of the composition claimed in claim 1.

HUGO L. SCHAEFER.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS In outdoor 

